Conventionally, there are flexible tubes for automobile exhaust systems available, for example, the flexible tube disclosed in the Japanese Utility Model Laid-Open Application No. 47421/1991.
As shown in FIG. 10, the conventional flexible tube is provided with the cylindrical shell 105 through the wire mesh 111 over the entire outer peripheral of the bellows 103, and further with the wire mesh 111 disposed in a labyrinth construction formed with the collars and the folded portions of the shell 105.
For tension, compression, bending and other possible forces to be applied on the flexible tube, the elasticity of the wire mesh 111 filled in between the shell 105 and the bellows 103 can moderately limit the deformation of the bellows 103, thus increasing the service life of the flexible tube. Further, the solid shell 105 covering the outer periphery of the bellows 103 can prevent the bellows 103 from damaging by kicked pebbles during car running. The labyrinth construction located at both longitudinal ends of the bellows 103 and provided with the wire mesh 111 can prevent muddy water from entering.
However, the conventional flexible tubes for automobile exhaust systems have following problems:
(1) Since the wire mesh may also elastically deform along with the deformation of the bellows to moderately limit the deformation magnitude of the bellows for a displacement input of the bellows, the total spring constant of the flexible tube may depend on the sum of the spring constants of the bellows and the wire mesh, thereby being increased as the displacement increases. Further, the wire mesh covering the outer periphery of the bellows may increase the spring constant of the bellows for compression force, if the wire mesh should enter into the root clearance of the bellows due to its partial deformation or partial loosening.
In other words, the desirable displacement absorption of the bellows largely depends on how the wire mesh is properly arranged, thus necessitating the need for controlling the filling process of the wire mesh.
Therefore, when filling the wire mesh around the entire outer periphery of the bellows to have the displacement absorption capability which can moderately restrict an unexpected deformation of the bellows, the spring constant of the bellows must be previously set as low as to prevent an abnormal rise in the spring constant of the flexible tube due to an improper arrangement of the wire mesh. This means the necessity of the larger total number of bellows, thus resulting in a larger size and weight of the flexible tube.
(2) Even if, at the initial installation, the wire mesh is uniformly distributed in between the shell and the bellows, repetitive and irregular application of tension, compression, bending and other forces on the wire mesh during service may cause an irregular (dense and thin) displacement of the wire mesh.
Therefore, it may become difficult during the service life to control the maximum displacement limitation of the elongation, contraction and flexure of the bellows in a stable manner. Nevertheless, a smaller maximum displacement limitation means a lower displacement absorption, and a larger maximum displacement limitation means a shorter longevity of the bellows.
(3) In this case, the positioning of the shell is made by the charged wire mesh, thus resulting in a larger number of charging man hours or a larger cost.
(4) The inner side of the bellows is directly subject to the high temperature of exhaust gas, so that an extended duration of car running or running under a heavy load may cause an extremely high temperature of the bellows, which may tend to bring about material change or high-temperature salt contamination or corrosion of the bellows, thus resulting in a shorter longevity of the bellows.
Further, with a conventional type of the flexible tube (disclosed in the Japanese Utility Model Laid-Open Application No. 69320/1994), a flexible casing (what is called inner blade) made of stainless fine wire fabric is installed inside the bellows 103 so as to protect the bellows from exhaust gas.
However, this inner blade is not only of high cost, but also may deform due to contact to the bellows when the flexible tube is under force, thus not only resulting in increment of cost of the flexible tube, but also causing an increased spring constant of the bellows under flexure.
Considering the solution of the above problems, this invention has been made.
The first target of the invention is: With an automobile exhaust system having a bellow assembly (bellows) therein to absorb the displacements of the first exhaust pipe and the second exhaust pipe to be installed in the automobile exhaust system, the flexible tube according to the invention consists of a small-sized lightweight configuration without using the conventional wire-mesh filling construction, thus achieving a low cost, good control of a stable elongation displacement limitation, and an increased longevity of the bellows as well as an enhancement in displacement absorption capability in bending and shearing directions.
The second target of the invention is: To achieve the first target, while the flexible tube according to the invention maintains the maximum displacement limitation function of the bellows in the contraction direction.
The third target of the invention is: To achieve the first or second target, while the flexible tube according to the invention not only suppresses a significant rise in construction cost as far as possible when a casing is to be installed inside the bellows so as to prevent the bellows from being affected by exhaust gas, but also prevents a rise in spring constant of the bellows when the flexible tube is subject to flexure.
The fourth target of the invention is: To achieve the first or second target, while the flexible tube according to the invention suppresses the thermal effect of exhaust gas to the bellows.